In general, if some of the Premium practice tests are still locked after the upgrade, it could be due to the relative recency of your purchase, so hard-refreshing the page should help.
Steps to follow:
Refresh: Press Ctrl+R (simultaneously) or Ctrl+F5 on your Windows computer, or Command (⌘)-R on a Mac.
Check if you're signed in: Check if you can see your name in the top right. If not, you're signed out and need to sign back in (depending on your browser settings, your session could have timed out). To sign back in, click the "Premium login" link. Enter the e-mail and password you used during registration. You can also sign in by clicking this direct link: https://cna.memberful.com/auth/sign_in
Switched devices? Sign in: If you purchased from a mobile device, but are trying to practice on a desktop computer, there is no way for us to know you have upgraded. In this case, you need to sign in on all new devices you would like to keep practicing on. Please see the steps above.
Send us an email: If none of the above helps, send us an email at email@example.com, and we'll get back to you as soon as we can!